Farnham maxwell lyte



UNITED STATES PATENT OFFICE.

FARNHAM MAXWELL LYTE, OF LONDON, ENGLAND,'AND GEORGE LUNGE,

OF ZURICH, SWITZERLAND.

PROCESS OF MAKING CAUSTIC ALKALI AND LEAD CH LORID.

SPECIFICATION forming part of Letters Patent No. 514,125, dated February 6, 1894.

Application filed August 23, 1893. Serial No. 483,806- (No specimens.) I V duction of Caustic Alkali and Chlorid of Lead for Conversion into Chlorin and Refined Lead, of which the following is a full, clear, and exact description.

This invention relates to improvements in that part of the process forming the subject of Patent No. 481,407 whereby caustic alkali and chlorid of lead are produced (the latter for conversion by electrolytic decomposition into chlorinand refined lead) from an alkaline chlorid and crude lead. In the'process as therein described, nitric acid plays the part of avehicle for lead and the intention of the patentee is that it shall be continuously recovered for use over and over again, but it has been found in practice that the recovery of the nitric acid is very incomplete and the consequent loss of nitric acid which ensues is a commercial disadvantage of the aforesaid process, which it is the object of the present invention to remedy. 1

In the process above referred to oxid of lead is dissolved in nitric acid to form nitrate of lead, with which and with an alkaline chlorid, say common salt for example, nitrate of soda and chlorid of lead are formed by double decomposition. If potassium chlorid be employed caustic potash will be produced and therefore wherever in the following description soda is mentioned, potash must be understood also. On heating the alkaline nitrate in admixture with an equal amount (or less) of ferric oxid as in the aforesaid process, the nitrate is entirely decomposed and a compound of ferric oxid and soda is formed which is known as ferrite of soda, nitrous fumes being evolved. But although the whole of the nitrate of soda can be decomposed in this way, the recovery of the nitric acid is very incomplete, owing to the fact that the fluxing of the mass renders such a high temperature necessary to effect the decomposition of the nitrate of soda as to cause the splitting up of a considerable quantity of the nitrogen oxide too-far for recovery as nitric acid.

This invention has for its object to overcome this objection and it consists in maintaining the mass in aporous condition throughout the operation so as to render it easily permeable, heating it not only externally but also internally by subjecting it to the action of a mixed current of heated air and steam whereby complete decomposition is effected and the evolution of nitrous fumes wholly or almost wholly convertible into nitric acid is rendered possible, at a much lower temperature than when the fiuxing 0f the mass into a mixed solid and liquid condition is permitted.

In carrying out the process such aquantity of ferric oxid is intimately mixed with the nitrate that the resulting mass will not fuse at the temperature of the reaction, but will remain solid and porous throughout the operation of decomposition. The nitrate being in solution the mixing of the ferric oxid with it may be advantageously effected while evaporating the solution to dryness so as to effect a uniformly intimate mixture. The mass remaining porous when heated is easily permeable by the mixed current of heated air and steam which is forced through it in any convenient way, suitable provision being made for the collection of the nitrous fumes and their conversion into nitric acid. It has been found when employing ferric oxid in the shape of purple ore that the best proportion is about two parts thereof by weight to one of nitrate of soda, but the invention is not limited to that particular quality of ferric oxid, nor to that particular proportion, as'it may be possible, according to the physical state of the ferric oxid, its degree of division, &c., to use less than the proportion indicated, but the quantity must always be sufficient to prevent any fluxing of the mass. It is not, however, sufficient to thus prevent the fluxing of the mass but it is also essential tolower the temperature of the decomposition sufficiently to enable the nitrous fumes evolved to be wholly recoverable or nearly so, as nitric acid, and this is effected by subjecting the mass to the intimate action of a mixed current of heated air and steam. The mixed current of air and steam should be heated preferably to the same temperature as that of the mass, say to a degree corresponding to an incipient red heat, to wit, between about 450 and 550 centigrade for the best results, although any temperature between 300 and 7 00 centigrade will suffice, and when the heated current is passed through the porous mass obtained by mixing nitrate of soda and ferric oxid as above mentioned, a dirty green mass is formed consisting essentially of ferrite of soda, with evolution of nitrous fumes, the temperature at which the decomposition is effected being such that most of the nitric acid corresponding to the nitrite of soda used is recoverable by air and water in the ordinary way, no sodium nitrate or nitrite remaining, and only a very slight proportion of the oxids of nitrogen being destroyed. Steam alone is unsuitable, even it' superheated, and although hot air alone acts better than steam, a mixture of air and steam previously heated to the temperature which prevailsin the decomposing retort gives much the best results. The quantity of steam is regulated in such manner that the recovered nitric acid is not too weak and the quantity of air is kept in due excess for reconverting the lower oxids of nitrogen into nitric acid by means of a Lunge tower or other suitable contrivance. The resulting ferrite is to be decomposed by heating it with water whereby ferric oxid is precipitated for use over again and the alkaline base enters into solution from which it is recovered as caustic soda by evaporation in the ordinary Way.

It is to be observed that the liquor which results after mixing a solution of equivalent quantities of lead nitrate and alkaline ch10- rids and filtering from the chlorid of lead separated, still contains a somewhat considerable quantity of lead chlorid dissolved. We concentrate this liquor to such a point that as much as possible of the lead chlorid crystallizes outon cooling Without any sodium nitrate crystallizing out at the same time. The lead then still remaining in solution is precipitated by adding an equivalent proportion of an alkali or an alkaline earth.

Having now particularly described and ascertained the nature of the said invention and in what manner the same is to be performed, we declare that what we claim is- 1. The herein described process of forming caustic alkali and chlorid of lead from an alkaline chlorid and oxid of lead, which process consists in first forming an alkaline nitrate by the double decomposition of nitrate of lead and an alkaline chlorid, and then decom posing the alkaline nitrate thus formed while in admixture with ferric oxid in sufiieient proportion to maintain the porosity of the mass by subjecting the mass to the action of heated air and steam at a temperature suiiicient to convert the whole of the base of the alkaline nitrate into a ferrite of the alkali with the evolution of nitrous fumes, substantially as specified.

2. The herein described process of forming caustic alkali and chlorid of lead from an al-' kaline chlorid and oxid of lead and of recovering the nitric acid used as a vehicle for the lead, which process consists in first forming an alkaline nitrate by the double decomposition of nitrate of lead and an alkaline chlorid, in then decomposing the alkaline nitrate thus formed while in admixture with ferric oxid, by subjecting the mass to the action of heated air and steam at a temperature sufficient to convert the whole of the base of the alkaline nitrate into a ferrite of the alkali with the evolution of nitrous fumes, and in then converting the said nitrous fumes into nitric acid, substantially as specified.

FARNHAM MAXWELL LYTE. GEORGE LUNGE.

Witnesses as to the signature of Farnham Maxwell Lyte:

M. HANDFORD, Finboro Road, London, Savant.

W. M. HARRIS, 17ZGracechm-ch Street, London, N 015cm] Pub- 10. Witnesses as to the signature of George Lunge:

K. GEINEMANN,

Zurich, Oheim'st. 'l. GLOOR,

Zurich, Clerk. 

